I think that depends entirely on the relationships. I imagine that there can be relationships between people that are entirely vanilla which are tremendously deep and meaningful and others which aren't. There can also be amazingly deep and meaningful M/s relationships and others that are less so.

At the end of the day if both parties are really open, honest, compatible and really in love with each other then I don't think it matters the context in which their relationship takes place. That said, I don't think I could have as meaningful a relationship with someone in a completely vanilla context than I could with certain BDSM elements but that's because for me it makes up and important part of the chemistry. There would be a level of intimacy not present and a compatibility that would be absent that I would want.

But that's just me and your mileage may vary.

-Geoff